The case study presented involves a migration from custom database to WordPress. The company with the task is Valet and it has a vast portfolio of previously done jobs that included shifts from database to WordPress, multisite-to-multisite, and multisite to single site among others. The client is Shift.ms.

Problem

The client, Shift.ms, presented a taxing problem to the team. Shift.ms had a custom database that they needed migrated to WordPress. They had installed a WordPress/BuddyPress and wanted their data moved into this new installation. All this may seem rather simple. However, there was one problem; the client had some data in the newly installed WordPress that they intended to keep.

Challenges

The main problem was that the schema for the database and that of WordPress are very different in infrastructure. The following issues arose in an effort to deal with the problem:

This is a guest post by Ashwanth Fernando, Software Engineer from the trenches at large scale internet companies.

Inspired by the book "Effective Java" by Joshua Bloch, I wanted to share my holistic recommendations on building high traffic web software (i.e. web applications/services that serve high traffic loads). Some of these items may not be just about software design but also around surrounding areas such as the engineering organization, culture etc.

Two disclaimers up front:

1) This is my opinion.2) There will be real world situations where the below principles will be wrong as in all things "software". Please use common sense all the time.

Consider using more than one datacenter

There have been numerous horror stories about businesses, ahem going out of business because they just had a single datacenter. Its really important to have more than one data center if you want to protect yourself from natural disasters or electrical supply failures. Run all your datacenters in active-active configuration. It may cost extra money, but its well worth it rather than having an active passive configuration and then finding out at the end that for some pieces of data, your passive hardware was not consistent with the active one.

Some of us are not aware of the tremendous job databases perform, particularly their efforts to maintain the Isolation aspect of ACID. For example, some people believe that transactions are only related to data manipulation and not to queries, which is an incorrect assumption. Transaction Isolation is all about queries, and the consistency and completeness of the data retrieved by queries. This is how it works:

Current disk based RDBMS can run out of steam when processing large data. Can these problems be solved by migrating from a disk based RDBMS to an IMDB? Any limitations? To find out, I tested one of each from the two leading vendors who together hold 70% of the market share - Oracle's 11g and TimesTen 11g, and IBM's DB2 v9.5 and solidDB 6.3.